1. Field of the Invention
The invention concerns a signalling device particularly designed for a motor vehicle. It concerns, for example, a signal light, a flashing light, arranged to the front or rear of a vehicle, or a parking light or brake light.
2. Description of the Related Art
More particularly, it concerns signalling devices which generate an effect of three-dimensional depth thanks to a particular optic device. Such a device is known by the patent document EP 1 916 471 A1, which is equivalent to U.S. Patent Publication 2008/0094872, which is incorporated herein by reference and made a part hereof. This document describes a sidelight comprising a cavity formed by a reflector and a screen arranged away from the reflector. The screen has the particular feature of being semi-reflecting, that is, some of the luminous rays that meet it are reflected, and others are transmitted. The cavity presents the particular feature that one of the surfaces of the reflector and the screen of which the cavity consists, is convex.
A series of light sources of the electroluminescence diode type is arranged at the periphery of the reflector, and directed so as to emit the light generally towards the screen. Given its semi-reflecting nature, some of the light rays are directly transmitted and some are reflected towards the reflector. The reflector then reflects these rays towards the screen with a gap directed towards the center of the reflector. These rays reflected by the reflector meet the screen again. Similarly to the light rays originating directly from the light sources, some of the rays are transmitted by the screen and some are reflected towards the reflector, and so on. These multiple partial transmissions and partial reflections result in an optical effect of depth in three dimensions.
The power of lighting or illumination of the emitted light rays decreases progressively in accordance with the reflections in the cavity. This optical effect is interesting as it enables the sidelight to be customized to draw the attention of other drivers. It also allows the sidelight to be concealed within a bodywork element, such as a bumper or a motor vehicle wing. It also allows the completion of a slim signalling device of small overall dimension with respect to the effect of depth generated. In effect, the semi-reflecting nature of the screen is obtained by applying a metallic coating which may give it a metalized appearance similar to that of a bodywork element.
The teaching of this document, however, presents one major disadvantage, that is, the treatment of the screen which is intended to make it semi-reflecting. The metallic layer applied on the screen will have the consequence that some of the rays originating from the light sources will be transmitted (without counting the losses inherent in the material of the screen). The rate of reflection and transmission may vary and will be directly dependent on the application of the metallic layer. From a point of view of procedure, it is very difficult to guarantee a rate of reflection and transmission within a narrow tolerance range. The consequence is that in the absence of a costly screen treatment procedure, the sidelight equipped with a light source of standard power risks not fulfilling the photometric conditions required by legislation for a signalling function and also risks making the left and right parking lights of the vehicle appear to be different.